Adapted from Orangette
I used Dufour brand puff pastry, which is pricey, but once you try it you’ll agree that it’s worth the expense. [Updated 12/20/18: Around the holidays, US folks can get their hands on fantastic Trader Joe’s puff pastry, which I every bit as good as Dufour at about a third of the price. I recommend stocking up—the pastry should last up to 6 months in your freezer.]
5 to 6 large apples, preferably Golden Delicious or Ginger Gold
Juice and finely grated zest of 1 lemon
1½ cups (300 g) granulated sugar
6 tablespoons (90 g) unsalted butter, divided
About 14 ounces (about 400g) puff pastry (if frozen, let it thaw for 1 hour at room temperature before using )
Peel, core, and quarter the apples. Cut the corners of the quarters so they have a beveled edge. In a large bowl, combine the the apple quarters with the lemon juice and zest, and ½ cup (100 g) of the sugar, toss together to evenly coat, and set aside for 30 minutes. The apples, combined with lemon juice and sugar, will give some juice.
Set a 9-inch (23 cm) cast-iron skillet over medium heat and melt 4 tablespoons (60 g) of butter. To the melted butter (be careful not to burn) add the remaining 1 cup (200 g) sugar, along with a few tablespoons of the apple-lemon juice*. Stir to mix until combined. Cook the mixture over medium-low heat, stirring regularly with a wooden spoon, about 15 minutes, or until the mixture is a smooth, pale golden-brown caramel, like the color of honey.
Immediately, remove the pan from the heat. Carefully, as not to burn yourself, place the apple quarters rounded side-down in a circular pattern. Arrange a second layer of apples on top wherever they fit. Dot the apples with the remaining 2 tablespoons (30 g) of butter, cut into tiny dice.
Preheat the oven to 375°F (190°C).
Cook the apples over medium-low heat for about 20 minutes, until they start to soften. Spoon a bit of the caramel over the apples, pressing down gently, from time to time. Make sure the caramel and apples cook pretty evenly throughout—and shift the pan as necessary. When the caramel turns dark amber and thick, remove the pan from heat. The apples should still be slightly firm, but showing some softness about the sides.
On a lightly floured surface, roll out the puff pasty about 3/16-inch thick. With a knife and a 10-inch wide parchment paper circle, cut out your pastry shell.
Carefully, as not to burn yourself, lay your pastry circle over the apples, and tuck the overlap between the apples and the inside of the pan. I found that using a fork to tuck the ends in was helpful.
Place the tart on a rimmed baking sheet and bake the tart for 30 to 35 minutes, until the pastry is golden brown. Remove the skillet from the oven and allow the tart to rest for a couple of minutes. Tilt the pan slightly, and if you see a lot of juice, pour most of it out. A little juice is useful—or the apples might stick to the bottom of the pan.
Place a serving platter over the skillet. With a decisive motion, both hands placed firmly on the 9 o’clock and the 3 o’clock, holding down the plate to the pan, flip the pan over so that the plate is now on the bottom. Gently set the plate down and remove the skillet. Your tart should easily separate from the pan onto the serving plate.
Serve warm or at room temperature. The tart is best the day it is made.
*You’ll have leftover sugar-apple-lemon syrup once you place the apples in the pan. It makes for a lovely simple syrup for cocktails, just so you know. Don’t throw it out!